1. Field of the Invention
The present invention relates to a method for producing a helical spring and an apparatus for producing the same, and more particularly to the method for producing the helical spring by cold working, and the apparatus for producing the same.
2. Description of the Related Arts
As for methods for producing helical springs, a method for producing the same by cold working and a method for producing the same by hot working are known heretofore. Various types of coiling machines are on the market for use as a machine for producing the helical springs by the cold working. In Japanese Patent Laid-open Publication Nos. 6-106281, 6-294631, 7-248811 and 9-141371, for example, the coiling machines are disclosed, and processes for controlling them are proposed. The basic structure of those machines is provided for bending and twisting an element wire while feeding the wire, to produce the helical springs, and it has been proposed to improve the machine accuracy by means of numerical control (NC). On the other hand, in accordance with recent progress of analytic technology, it is now possible to perform various simulations with respect to a certain spring-shaped model, and to design products on the basis of the result of the analysis. For example, it is possible to design a configuration of a spring having a certain characteristic, through FEM analysis.
In the case where the helical springs are manufactured by the coiling machines, however, mainly employed is a so-called try and error method for producing a helical spring temporarily and forming it in a certain configuration, with the dimensions of the temporarily formed spring being checked. In other words, although the coiling machines are driven according to the numerical control (NC), the data are input into the machines in dependence upon intuition or knack of operators. Therefore, measurements are made partially, so that overall configuration of the product can not be ensured, to cause such a problem that if its configuration is complex, the time for producing a prototype will be prolonged.
According to the machine disclosed in the Japanese Patent Laid-open Publication No. 7-248811 as described above, it is proposed to identify a part of the data to be corrected and confirm the data easily, in view of a prior automatic programming machine for use in a helical spring forming machine. In that publication, it is stated that the configuration of the helical spring produced by the prior machine was slightly different from the configuration of the designed spring in general, so that it was necessary for the operator to identify the part of the configuration to be corrected on the basis of the image obtained through the data shown on a display, whereby an error was likely caused. In order to solve the problem as described above, it is proposed that the configuration of the spring is shown on the display, then markers indicative of the part of the data to be corrected, and integrated number of coils (or turns) are displayed, and that the data are input by the operator, watching the configuration of the spring.
Also, improvements have been made with respect to the control of the coiling machines, as described in the above publications, but they are limited to the improvements from the view point of controlling the machines, so that they have not reached to a level of creating a working process for forming the objects to be worked into those of desired configurations, which can be done by an ordinary machinery working process. This is because the problem is resulted from specific issues on the helical spring as follows:
At the outset, when the helical spring is produced by the cold working, an elastic deformation is necessarily caused, to create a spring-back. Therefore, it is difficult to estimate a position of a working tool, and an appropriate distance to move the same, unlike a cutting process and so on. In addition, the amount of spring-back is varied in dependence upon hardness of the element wire, and the configuration of the helical spring. Especially, the manufactured compression helical spring is likely to cause a contact between the neighboring coils, so that it was very difficult to ensure a desired spring characteristic. In view of those matters, generally employed is a method for obtaining the NC data by checking the measurements of the actual products of prototypes.
Furthermore, the dimensions provided when designed and the dimensions formed by the coiling machine do not coincide with each other. For example, comparing with diameters of coils which are provided to indicate a desired configuration on a three-dimensional coordinate when the spring is designed, the diameters which are provided when the spring is formed are to be made larger, by a distance moved in the axial direction according to a lead. In addition, the feeding amount of the element wire (material) and the number of coils when worked (positions to be worked) do not coincide with each other, to cause a phase difference between the feeding amount of the element wire and bending positions or twisting positions. The number of coils as described above is used for identifying the position to be worked, from the coil end for example. Also, after the spring was formed by the coiling machine, generally a temper-treatment (low-temperature heat-treatment, hereinafter simply referred to as heat-treatment) is made to the spring, so as to cancel working stress applied thereto. Therefore, it is necessary to estimate a change in configuration of the spring, before working it.
From the foregoing reasons, it was impossible in the prior arts to accurately identify the actual position of the target to be formed, which should correspond to the position of the desired configuration on the coordinates. Therefore, the prototype was made by workers in dependence upon their intuition and knack, so that the spring was produced by a repetition of the try and error. As a result, the coiling machine capable of performing the numerical control could not be operated to fully use its inherent function, so that its operation was not far beyond a range of manual operation.
Accordingly, it is an object of the present invention to provide a method for producing a helical spring by cold working, with an element wire bent and twisted while the wire being fed, wherein a target helical spring of a desired configuration set in advance can be produced automatically and accurately.
It is another object of the present invention to provide a method for producing a helical spring by cold working, with an element wire bent and twisted while the wire being fed, wherein a target helical spring of a deformed configuration set in advance can be produced automatically and accurately.
And, it is a further object of the present invention to provide an apparatus for producing a target helical spring of a desired configuration including a deformed configuration set in advance, automatically and accurately.
In accomplishing the above and other objects, a method for producing a helical spring comprises the steps of providing a plurality of parameters for defining a desired configuration of a target helical spring, setting at least bending positions and twisting positions on the basis of the plurality of parameters, and bending and twisting the element wire at the positions set in response to every predetermined feeding amount of the element wire, to produce the target helical spring. In this method, preferably, the parameters includes number of coils, coil diameter and lead of the target helical spring.
The method as described above may further comprise the steps of applying a predetermined after-treatment to the helical spring produced by bending and twisting the element wire, and correcting the bending positions and twisting positions set on the basis of the plurality of parameters, in accordance with the configuration of the helical spring with the after-treatment applied thereto.
The method as described above may further comprise the step of adjusting at least the bending positions in response to the cycle of alternating diameters between a local maximum diameter and a local minimum diameter of the target helical spring.
According to the present invention, an apparatus for producing a helical spring by cold working to bend and twist an element wire while feeding the wire includes a parameter setting device which is adapted to provide a plurality of parameters for defining a configuration of a target helical spring, a data converting device which is adapted to convert the plurality of parameters provided by the parameter setting device into at least bending positions and twisting positions, a working conditions setting device which sets at least the bending positions and twisting positions in response to the result converted by the data converting device, a feeding device for feeding the element wire, a bending device for bending the element wire fed by the feeding device, and a twisting device for twisting the element wire fed by the feeding device. And a driving device is provided for driving the feeding device, the bending device and the twisting device, to place the element wire at the positions set in response to every predetermined feeding amount of the element wire, on the basis of the bending positions and twisting positions set by the working conditions setting device, then bend and twist the element wire, to produce the target helical spring.
The apparatus as described above may further include an adjusting device for adjusting at least the bending positions in response to the cycle of alternating diameters between a local maximum diameter and a local minimum diameter of the target helical spring, and the working conditions setting device is adapted to set at least the bending positions and twisting positions in response to the result converted by the data converting device and the result adjusted by the adjusting device.